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555-605 (Medium)|   Geometry|                                 
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Video solution from Quant Reasoning:
Subscribe for more: https://www.youtube.com/QuantReasoning? ... irmation=1
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In line to Bunuel's solution, we can also solve it using exterior angle and vertical angle properties. The sum of all exterior angles for a polygon is 360. So x+y = 360 - (w+z), and both 1 and 2 together provide the same.
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Bunuel

What is the value of x + y in the figure above?

Sum of Interior Angles of a polygon is \(180(n-2)\) where \(n\) is the number of sides (so is the number of angles). So, the sum of the interior angles of a quadrilateral is 180*2=360. Look at the diagram below:
Attachment:
Angles2.png
According to the above: (180-x)+(180-y)+(180-z)+(180-w)=360 --> x+y=360-w-z, so all we need to know is the values of w and z.

(1) w= 95. Not sufficient.
(2) z = 125. Not sufficient.

(1)+(2) Sufficient.

Answer: C.

If (180-w) = a and (180-z) = b, then the below generalized form is always true for any quadrilateral:
a+b=x+y

Maybe we can call it exterior angle theorem for quadrilaterals.
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Bunuel


Sum of Interior Angles of a polygon is \(180(n-2)\) where \(n\) is the number of sides (so is the number of angles). So, the sum of the interior angles of a quadrilateral is 180*2=360. Look at the diagram below:
Attachment:
Angles2.png
According to the above: (180-x)+(180-y)+(180-z)+(180-w)=360 --> x+y=360-w-z, so all we need to know is the values of w and z.

(1) w= 95. Not sufficient.
(2) z = 125. Not sufficient.

(1)+(2) Sufficient.

Answer: C.

How did you get from (180-x)+(180-y)+(180-z)+(180-w)=360 to x+y=360-w-z?

I am getting the following:

(180-z)+(180-w)=-180+x-180+y+360
-z-w=x+y+360
x+y=-360-z-w

Can you show more detail? Thanks in advance
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Bunuel


Sum of Interior Angles of a polygon is \(180(n-2)\) where \(n\) is the number of sides (so is the number of angles). So, the sum of the interior angles of a quadrilateral is 180*2=360. Look at the diagram below:
Attachment:
Angles2.png
According to the above: (180-x)+(180-y)+(180-z)+(180-w)=360 --> x+y=360-w-z, so all we need to know is the values of w and z.

(1) w= 95. Not sufficient.
(2) z = 125. Not sufficient.

(1)+(2) Sufficient.

Answer: C.

How did you get from (180-x)+(180-y)+(180-z)+(180-w)=360 to x+y=360-w-z?

I am getting the following:

(180-z)+(180-w)=-180+x-180+y+360
-z-w=x+y+360
x+y=-360-z-w

Can you show more detail? Thanks in advance

\((180-x)+(180-y)+(180-z)+(180-w)=360\)

\(720 - x - y - z - w = 360\)

\(360 - x - y - z - w=0\)

\(360-w-z=x+y\)
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Walkabout

What is the value of x + y in the figure above?

(1) w= 95
(2) z = 125

Attachment:
Angles.png
Solution:

We need to determine the value of x + y. We see that x and y are two of the exterior angles of the quadrilateral, and w and z are the other two exterior angles. Notice that x + y + w + z = 360 since the sum of the measures of the exterior angles of a polygon is always 360 degrees. Therefore, if we know the values of both w and z or if we know the value of w + z, then we can determine the value of x + y.

Statement One Alone:

Since we don’t know the value of z, statement one alone is not sufficient.


Statement Two Alone:

Since we don’t know the value of w, statement two alone is not sufficient.

Statements One and Two Together:

Recall that that x + y + w + z = 360; therefore, we have:

x + y + 95 + 125 = 360

x + y + 220 = 360

x + y = 140

Both statements together are sufficient.

Answer: C
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Question - if the y angle measure was actually placed on the top right corner of the polygon, answer would be E, right?
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Question - if the y angle measure was actually placed on the top right corner of the polygon, answer would be E, right?

Yup, you'd be able to find the value of (x-y) in that case and not (x+y).
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Bunuel

Can we consider x+w =180 only when lines are parallel?

Thanks!
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Bunuel

Can we consider x+w =180 only when lines are parallel?

Thanks!
______________________________________________________
Yes.
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